The Automatic Protection Switching (APS) is a necessary technology for the ring network. The ring network needs to use the APS technology to guarantee the least loss of the user information when the physical link becomes invalid or the signal transmission quality deteriorates.
The Synchronous Digital Hierarchy (SDH) network is a kind of comparatively mature optical network and has been in use for more than ten years. The information transmission technologies of SDH network have been fully used in the field of information transmission. Among the information transmission technologies of SDH network, the Multiplex Section Protection (MSP) is the most distinctive and practical technology. It uses k bytes in the SDH multiplex section, i.e. two overhead bytes k1 and k2 to transmit the protection switching information of the APS, i.e. the signalling of the APS protocol, wherein the two overhead bytes k1 and k2 occupy two bytes in all. All the network elements that received the SDH multiplex section will process the APS protocol signalling in the two overhead bytes of the SDH multiplex section so as to implement APS for the services in the ring network.
The G.841 protocol is an international standard on the switching of the multiplex section instituted by the Telecommunication Standardization Sector of ITU (ITU_T) and describes in detail the coding of the k bytes and the switching rule of the MSP technology and provides a comparatively complete switching rule. The G.841 protocol is a basis for realizing protection for the ring network. The G.841 protocol allocates the switching request field, the requested destination network element field, the requested source network element field, requested long or short path flag field and the switch status field in the k bytes.
Although currently the G.841 protocol provides the comparatively complete switching rule, there still exist some problems which make it difficult to accomplish the protection switching of the ring network.
The optical transport network (OTN) technology is also proposed. This technology is a newcomer in the transmission field and mainly introduces some mechanisms of SDH in the wave division field.
The OTN technology also introduced the most distinctive and practical technology of the SDH technology, i.e., the MSP technology. Specifically, the overhead bytes in the Optical Channel Data Unit-k (ODUk), i.e. the APS/PCC are used to transmit the protection switching information of the APS, i.e. the APS signaling, and the overhead bytes occupy four bytes.
Since the ring network protection technology for the OTN adopts the SDH multiplex section protection mechanism, the same problem as that in the SDH APS exists, i.e. the ring network protection technology for the OTN cannot perform a well protection switching for the OTN network.